The present invention relates to an electrochemical fuel cell assembly including a cell voltage monitor; and more particularly to an electrical connecting device which may be used to monitor individual cells or clusters of cells within a stack.
Fuel cells have been used as a power source in many applications. Fuel cells have also been proposed for use in electrical vehicular power plants to replace internal combustion engines. In proton exchange membrane (PEM) type fuel cells, hydrogen is supplied to the anode of the fuel cell and oxygen is supplied as the oxidant to the cathode. PEM fuel cells include a xe2x80x9cmembrane electrode assemblyxe2x80x9d (MEA) comprising a thin, proton transmissive, non-electrically conductive, solid polymer membrane-electrolyte having the anode on one of its faces and the cathode on the opposite face. The MEA is sandwiched between a pair of electrically conductive elements which (1) serve as current collectors for the anode and cathode, and (2) contain appropriate channels and/or openings therein for distribution of the fuel cell""s gaseous reactants over the surfaces of the respective anode and cathode catalysts. A typical PEM fuel cell and its membrane electrode assembly (MEA) are described in U.S. Pat. Nos. 5,272,017 and 5,316,871, issued on Dec. 21, 1993 and May 31, 1994, respectively, and assigned to General Motors Corporation, assignee of the present invention, and having as inventors Swathirajan et al.
A plurality of individual cells are commonly bundled together to form a PEM fuel cell stack. The term fuel cell is typically used to refer to either a single cell or a plurality of cells (stack) depending on the context. A group of cells within the stack is referred to as a cluster. Typical arrangements of multiple cells in a stack are described in U.S. Pat. No. 5,763,113, assigned to General Motors Corporation.
In most fuel cell assemblies, current is drawn from the fuel cell stack via a pair of bus plates, one of which is positioned at each end of the fuel cell stack. The fuel cells are stacked between the bus plates, which are typically made of copper or coated copper. Very often individual cells of the stack are contacted for monitoring individual cell voltages or currents, and/or for control or charging/discharging purposes. In most cases, these electrical contacts are not intended to carry the entire stack current, but are capable of providing electrical connection to individual fuel cells or clusters within a stack.
In mass production, an electrical connecting device is needed which is easy to handle and to install, and which provides reliable electrical contact with certain components of a fuel cell stack. It may be desirable to provide, in a single device, groups of contacts that always communicate with the same type of fuel cell component within the stack, or which contact the fuel cell stack at regularly spaced intervals along the length of the stack.
One problem with monitoring individual fuel cells or clusters of cells within a stack is the difficulty of attaching an electrical connector to the electrically conductive elements. For example, for a fuel cell which is designed to generate significant power output, a large number of bipolar plates are provided which require a large number of connections. Perhaps more importantly these connectors are located in close proximity to each other, making it difficult to make electrical connections without short circuiting with adjacent bipolar plates. The stack may include cells at a spacing, for example, of ten cells per inch. Thus, there is less than about 2.5 millimeters between each bipolar plate. Consequently, making such individual connections can be a slow and tedious process.
In a first aspect of the present invention a connector for electrically connecting to a series of closely spaced edges for use in monitoring individual cells using bipolar plates of a fuel cell stack is provided. The connector includes an elongated elastomeric strip with electrical conductivity from a first side thereof to an opposing side thereof, but not having meaningful electrical conductivity in use along its elongated length. The first side of the elongated elastomeric strip is located against a plurality of closely spaced edges. The connector also includes a plurality of electrically conductive elements located against the opposing side of the elongated elastomeric strip in corresponding relationship with the plurality of closely spaced edges located against the first side of the elongated elastomeric strip. The connector also includes means for exerting a force to push the first side of the elongated elastomeric strip against the plurality of closely spaced edges to provide an electrically conductive path associated with each of the plurality of closely spaced edges which flows from the first side of the elongated elastomeric strip, through the elongated elastomeric strip to the opposing side thereof, and through the electrically conductive elements which is isolated from the electrically conductive paths of adjacent closely spaced edges.
In another aspect of the invention a connector for electrically connecting to a series of closely spaced edges for use in monitoring individual cells using bipolar plates of a fuel cell stack is provided. The connector includes an elongated elastomeric strip with electrical conductivity from a first side thereof to an opposing side thereof, but not having meaningful electrical conductivity in use along its elongated length; the first side of the elongated elastomeric strip being located against a plurality of closely spaced edges. The connector further includes a housing with an opening adapted to hold the elongated elastomeric strip. Also included is a printed circuit board having a plurality of electrically conductive elements located thereon, the printed circuit board being attached to the housing such that the electrically conductive elements are located against the opposing side of the elongated elastomeric strip in corresponding relationship with the plurality of closely spaced edges located against the first side of the elongated elastomeric strip. Additionally included is means for exerting a force to push the first side of the elongated elastomeric strip against the plurality of closely spaced edges to provide an electrically conductive path associated with each of the plurality of closely spaced edges which flows from the first side of the elongated elastomeric strip, through the elongated elastomeric strip to the opposing side thereof, and through the electrically conductive elements which is isolated from the electrically conductive paths of adjacent closely spaced edges.
In another aspect of the invention a method of providing an electrical connection to a series of closely spaced edges for use in monitoring individual cells using bipolar plates of a fuel cell stack is provided. The method includes the step of providing an elongated elastomeric strip with electrical conductivity from a first side thereof to an opposing side thereof, but not having meaningful electrical conductivity in use along its elongated length. Also included is the step of locating the first side of the elongated elastomeric strip against a plurality of closely spaced edges. Further included is the step of locating a plurality of electrically conductive elements against the opposing side of the elongated elastomeric strip in corresponding relationship with the plurality of closely spaced edges located against the first side of the elongated elastomeric strip. Additionally included is the step of exerting a force to push the first side of the elongated elastomeric strip against the plurality of closely spaced edges to provide an electrically conductive path associated with each of the plurality of closely spaced edges which flows from the first side of the elongated elastomeric strip, through the elongated elastomeric strip to the opposing side thereof, and through the electrically conductive elements which is isolated from the electrically conductive paths of adjacent closely spaced edges.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.